A drive unit is known, from the patent application EP-A-0968911, of which the present Applicant is proprietor, in the form of an assembly kit able to be applied on a bicycle, in order to make pedaling comfortable and easy for a user and prevent him from having to make excessive efforts.
The drive unit comprises as its essential parts an electronic control unit, an electric feeder, an electric motor and a motion transmission unit, which connects a flywheel of the bicycle to the electric motor.
The drive unit is also associated with a toothed ringnut that is connected to the pedals and is provided with a sensor able to detect the rotation of the ringnut and send a corresponding signal to the central command unit.
The motion transmission unit substantially comprises a reduction assembly, which is connected by means of a first free wheel to a pinion, in turn connected to a toothed wheel coaxial with the flywheel.
Moreover, a second free wheel is arranged between the pedals and the flywheel of the bicycle in order to render the motion of the latter independent when the motor is in action.
In the known drive unit, the motion transmission unit and the flywheel are not on the same axis of rotation, and hence the pinion and the toothed wheel are connected to each other by means of a transmission chain.
The known drive unit, although very efficient and functional, has the disadvantage that in its entirety it is complex and articulated, and also bulky, due to the misaligned position of the motion transmission unit with respect to the flywheel.
Moreover, it has been observed that the presence of a chain between the pinion and the toothed wheel makes the transmission of motion, as actuated by the electric motor to the flywheel, less easy and smooth.
The present Applicant has devised and embodied this invention to overcome this shortcoming of the state of the art and to obtain other advantages.